The schematic diagram of a conventional Heller-type cooling system or in other words that of an indirect dry cooling system is shown in FIG. 1. The cooling system comprises a direct contact condenser 11, which condenses the spent steam coming from a steam turbine 10 by means of cooling water re-cooled in an indirect dry cooling tower 12. The cooling water warmed up in the direct contact condenser 11 is supplied to the cooling tower 12 in a pipeline 15 by means of a cooling water pump 16 driven by a motor 17.
Heller cooling systems are known which comprise a so-called recuperative water turbine 18 built into the cooling water branch leading from the cooling tower 12 to the direct contact condenser 11. The major task thereof is to absorb usefully the elevating height (drop) which is not needed for returning the cooling water to the direct contact condenser 11. The power recovered on the water turbine 18 contributes to the operation of the motor 17 which drives the cooling water pump 16, thereby reducing the energy need of the motor 17. The motor 17 (electric motor) driving the cooling water pump 16 has two shaft ends. On one side it is coupled to the cooling water pump 16 and on the other side to the water turbine 18, thereby creating a water machine group running with a common axis. Such an approach is disclosed by way of example in the Hungarian patent specification 152 217.
The air flow (draught) necessary for heat transfer is provided by the indirect dry cooling tower 12. The draught can be a natural draught (chimney effect) and it can be an artificial draught (ventilator draught). Prior art cooling towers 12 have one or more heat dissipating units 13 which transfer the heat to be absorbed to the ambient air, and the cooling system also comprises a de-aerating structural component 14 which defines a de-aerating space coupled to the top of the flow space of the heat dissipating unit 13. Generally, prior art heat dissipating units 13 are triangular cooling units (cooling deltas) arranged horizontally or standing vertically along the periphery of the cooling tower 12, and are grouped into sectors, where triangular cooling units associated with a sector have a common cooling water inlet and common de-aerating structural component 14. The common de-aerating structural component 14 generally comprises a de-aerating circular line connecting the top of the triangular cooling units of a sector, and an upright extending de-aerating rack pipe known per se coupled thereto.
In the course of the operation of the conventional Heller-type cooling system, the spent steam coming from the steam turbine 10 is condensed by chilled cooling water supplied to the direct contact condenser 11. For the sake of improving the efficiency of steam recirculation, vacuum has to be ensured in the direct contact condenser 11. It is the cooling tower 12 of an appropriate cooling capacity which ensures to reach this vacuum. As a consequence of the condensation of the exhaust steam, the cooling water is warmed up in the direct contact condenser 11. The warmed up cooling water is removed from the vacuum space of the direct contact condenser 11 by the cooling water pump 16, which then supplies it to the rack pipes located on the top of the triangular cooling units.
The de-aerating rack pipes may even reach 6 to 8 m above the top of the triangular cooling units, and the cooling water level may be 1 to 2 m above the top of the triangular cooling units during operation. The de-aerating rack pipes are opened on the top and hence atmospheric pressure prevails above the cooling water.
The elevating height of the cooling water pump 16 has to be determined in such a way that the cooling water is raised from the vacuum in the direct contact condenser 11 to the atmospheric pressure in the rack pipe, furthermore from the water level of the direct contact condenser 11 to the much higher water level of the rack pipe in such a way that it overcomes the hydraulic resistance of the forward-going branch as well. The driving force of the cooling water flow returning to the direct contact condenser 11 is the pressure difference which prevails between the atmospheric pressure and the vacuum (steam condenser shell pressure) of the direct contact condenser 11, and furthermore the geodetic difference between the water level of the rack pipe and the water level of the direct contact condenser 11. This driving force overcomes the hydraulic resistance of the returning branch and the direct contact condenser 11. The available driving force is, however, much higher than that required for overcoming the hydraulic resistances. To absorb this extra driving power, generally a throttle valve or a much more cost efficient solution, the recuperative water turbine 18 mentioned above, is applied.
It is clear from the above disclosure of the conventional Heller-type cooling system that the cooling water pump 16 is not to be designed for overcoming the hydraulic resistance of the whole cooling water circuit, but for a higher load. Therefore, it is necessary to have the water turbine 18 so that the unnecessary elevating height (drop) can be utilised relatively cost efficiently (much more efficiently than by using throttle). However, the application of the water turbine 18 necessarily entails loss, too, resulting from the loss of the cooling water pump 16 and the water turbine 18.